This invention relates in general to the construction of breathing devices and in particular to a new and useful gas mask having an outer full mask and an inner half mask and with means for accommodating for leakage by increasing and decreasing the volume in the space between the masks during operation.
A known problem in respirators is their tight connection to the respiratory tracts of the wearer. The safest connection per se is the mouthpiece. However, it is not always pleasant to wear and requires a corresponding discipline of the wearer. Prevalent today is the full mask also with inner mask. The necessary tight connection, however, is achieved with it only if any leakage remaining due to the different face forms are compensated. It must be prevented in any event that air from the surrounding atmosphere can enter through the mask seal or also, as here in closed cycle respirators, that oxygen can issue, because of the fire hazard.
Known is a gas mask with double sealing edge which possesses means for passing exhaled air through the space between the two sealing edges. In the realization the double sealing edge is created by the seal at the full mask and at the inner mask, which covers also the entire face. Inhalation occurs through the connection piece directly into the inner mask. Exhalation occurs via a valve which opens in an exhalation direction in the wall of the inner mask through the interspace between the two masks, either through a further valve means directly to the outside or back into the closed cycle respirator. A slight pressure builds up in the interspace, so that, although when connected to a closed cycle respirator possibly unbreathable ambient air cannot enter the mask space through leakages, cycle air can flow out through the leaks in the sealing edge of the outer mask. This may lead to considerable shortening of the time the mask can be used, as this outflow volume must be replenished from the relatively small oxygen reserve of the respirator; because of the possibly high oxygen percentage, the outflow volume constitutes a great fire hazard. (Swiss Patent No. 473,592).
Known also is a gas mask with inner half mask for closed cycle respirators where through a positive pressure in the space between the two masks, the mask interspace, access of ambient air is prevented. The inner half mask is disposed in a full mask. The latter is in direct communication with the connecting piece which leads to the respirator and through which one inhales and exhales.
In its wall, the inner half mask has a check valve opening in the direction of the mask interspace. On exhaling into the cycle this valve opens, so that exhaled air can flow into the interspace up to the exhalation resistance of the respirator. A corresponding positive pressure is then created in the interspace relative to the surrounding atmosphere. During inhalation the check valve is closed. With the seal of the full mask and of the inner half mask this positive pressure is maintained. If there are slight leaks, it decreases to "zero" during the following inhalation phase. The next exhalation compensates the pressure drop.
However, it is very difficult to seal inner half masks as perfectly as the outer full mask. Thus, there is danger that the positive pressure will decrease too rapidly during the inhalation phase through pressure equalization to the interior of the inner half mask, and that consequently a positive pressure and hence a protection against leakages does not exist in the mask interspace during the entire inhalation phase. (DE-OS No. 30 15 761).